The present invention generally relates to an apparatus and method for detecting disconnection in a secondary side of a current transformer, and, more particularly, to a circuit and method that monitor the secondary side voltage of a transformer to determine if the secondary side is disconnected.
Current transformers (CT) typically are used in power applications such as power meters. A CT detects electric currents in a wire, and generates a signal proportional to the current. In power applications, the current in the primary side is too large to be safely measured. The CT can be used for generating a much lower and proportional current on the secondary side, which is suitable for measurement or protection. Because the secondary side current is proportional to the primary side current, the measured secondary side current can be converted to reflect the primary side current using the equation Kn=I1n/I2n, wherein Kn is a current ratio from the primary to the secondary, I1n is the primary side current, and I2n is the secondary side current. A CT thus provides safe electrical isolation.
A critical requirement for using a CT is that, when there is current in the primary side, the secondary side must be connected with a load instead of being open. If the secondary side is open, the primary side current will push the secondary voltage to an extremely high value, which can be harmful and dangerous.
It therefore would be advantageous to be able to detect if the secondary side of a CT is disconnected.